That exception seems to be thrown from the constructor of DataProviderBase and I get it even if I switch to TxtDataProvider. It doesn’t help that the same
binding works in other projects of the same solution :(

Version that worked before updating to 2015.1.0401.1050 NoXaml – 2014.3.1024.1050 NoXaml
All references set according to http://docs.telerik.com/devtools/silverlight/controls/radrichtextbox/getting-started/getting-started

Petya

The data providers rely on format provider instances registered when the control is loaded. This happens with the help of MEF and it is possible that the provider hasn't been registered yet. In previous versions of the control this would simply silently fail and the binding wouldn't work, but in the resent release we tried to make sure the users are notified about the error.

Try setting the TypeCatalog needed by MEF from this article and see if the issue persists.

Sergey

Thank you so much, that was indeed the issue!
We were initializing Telerik catalog inside of our own OnImportsSatisfied() which was too late.

One remaining minor issue in this release (or in our code?) is that we had to reference Telerik.Windows.Documents.dll in order to use txt provider and this dll exposes System.Serializable, so I had to use 'extern alias' to work around it.

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